Yes MAAS uses freeipmi-tools. According to the freeipmi-tools changelog support for IPMI cipher suites 15, 16, and 17 was added in 1.2.1 which was released on 08/22/12. Ubuntu Xenial 16.04 LTS and Ubuntu Bionic 18.04 LTS both have freeipmi-tools 1.4.11 while Ubuntu Focal 20.04 LTS has freeipmi-tools 1.6.4.
BMCs can be a bit inconsistent with their output and support which may be why cipher suite 17 shows up with ipmitool and not bmc-config.